Diseases of economic plants (1921) Diseases of economic plants diseasesofeconom01stev Year: 1921 Small Fruits 121 Upon the leaves the disease appears considerably earlier than upon the fruits. Here it produces tan-colored spots about 3-8 mm. in diameter, many or few according to the severity of the infection. In or near the centers of the older spots, upon the upper surface of the leaves, are seen the nearly microscopic pycnidia which are often arranged in concentric circles. On the young shoots the spots are somewhat more reddish and are often cracked longitudinally, but otherwise they are
Diseases of economic plants (1921) Diseases of economic plants diseasesofeconom01stev Year: 1921 Small Fruits 121 Upon the leaves the disease appears considerably earlier than upon the fruits. Here it produces tan-colored spots about 3-8 mm. in diameter, many or few according to the severity of the infection. In or near the centers of the older spots, upon the upper surface of the leaves, are seen the nearly microscopic pycnidia which are often arranged in concentric circles. On the young shoots the spots are somewhat more reddish and are often cracked longitudinally, but otherwise they are as upon the leaves. This rot is much more prevalent in warm, humid weather than in dry times, and a few days of muggy weather may so favor the growth of the causal fungus as to develop an epidemic, which may in turn be checked by a dry spell. Often the disease appears in distinct waves during the season, each wave cor- responding to a climatic condition favorable to infection and usually lagging behind such favorable con- dition a period of 8 to 14 days, the time necessary after infection for the disease to become conspicuous enough to attract the attention of the vineyardist. While the Scuppernong occa- sionally shows a few spots upon leaf or berry and the blossom is sometimes affected, this variety is practically immune. To prevent the inroads of black-rot, thorough, clean cul- ture should be practiced. All mummified fruit should be burned to avoid infection. Keep the ground free from sprouts and all other growths and permit no weeds or grass. Cover crops are beneficial. Plow early so as to cover all re- maining leaves and berries that bear the hibernating fungus. Fig. 61.—-Grape black- rot. Original.
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